1. Field of the Invention
This invention relates to an automatic transmission, and more particularly, to a shifting arrangement of an automatic transmission for an automotive vehicle which provides the driver with a manual choice of transmission gears in addition to automatic transmission gear selection.
2. Description of Related Art
Typically, automatic transmissions for automotive vehicles of a type having a gear range for manual selection in addition to an automatic gear range selection are in the process of being put to practical use. Such an automatic transmission is known from, for example, Japanese Patent Application, laid-open to the public as Japanese Unexamined Patent Application No.3-89075.
The automatic transmission described in the above mentioned publication has two shifting paths for a shift lever, namely a first or range shifting path for ordinary range selection which allows the shift lever to shift its position and select regular shift positions such as a park (P) position, a reverse (R) position, a neutral (N) position, a drive range (D) position, a third speed (3) position, a second speed (2) position and a first speed (1) position, and a second or gear shifting path in which the shift level can take three position, namely a neutral or center position, an up-shift position and a down-shift position. In the second shifting path, the shift lever is shifted to the up-shift position from the neutral position to shift one gear up. Similarly, the shift lever is shifted to the down-shift position, opposite to the up-shift position with respect to the neutral position, from the neutral position to shift one gear down. These first and second shifting paths are arranged side by side and in parallel with each other and interconnected to each other by a transverse change over path extending therebetween.
In this parallel type of shifting arrangement having two parallel shifting paths, various constraints are imposed on a design of the whole arrangement, the range of movement of the shift lever, which leads to difficulties in installing the automatic transmission including the shifting arrangement into the vehicle, and/or laying out it together with various peripheral devices in a limited space. In order to avoid some of these difficulties, it may be considered to arrange first and second shifting paths in series in the lengthwise direction of the vehicle so that the second shifting path has selective positions at one of the extreme ends in the first shifting path.
In any type of shifting arrangement, there is still a problem encountered by the shifting arrangement. Specifically, as described in the above mentioned publication, the shifting arrangement is provided with shift switches in the second or gear shifting path which are actuated by the shift lever placed at the up-shift position or the down-shift position, respectively, to cause an up-shift or a down-shift of the transmission gear. It is possibly caused that, in the event where an imprudent changing over of the shift lever is once caused from the first or range shifting path to the second or gear shifting path, one of the shift switches is accidentally actuated by the shift lever when returning the shift lever into the first or range shifting path again with the result of a shift of the transmission gear which is not intended by the driver. This accidental gear shift is encountered by, in particular, the parallel type of shifting arrangement. In order for the shifting arrangement to prevent from causing such an accidental gear shift, the shift lever is provided with a lock button for locking change over movement of the shift lever from the first shifting path into the second shifting path and allowing the change over movement only following unlocking operation of the lock button by the driver.
An unintentional gear shift is still possibly encountered by the shifting arrangement of the type having shift switches directly actuated by the shift lever even if which is even though provided with the lock button. For example, regardless whether the driver releases the lock button after changing over the shift lever to the second shifting path with an intention to cause a manual gear shift or whether the driver returns the shift lever back to the first shifting path holding the lock button operated with an intention to cancel a manual gear shift although having changed over the shift lever to the second shifting path with an intention to cause a manual gear shift, a manual gear shift is actually caused when the shift lever is shifted in any direction in the second shifting path and brought into contact with any one of the shift switches in the second shifting path. In the later case, in particular, the manual gear shift is accidental. In that point of view, installation of the lock/release button in any type of shifting arrangement, which is adapted to be manually operated by the driver, does not always provide a safety measure against accidental manual gear shifts.
With some automatic transmissions of the above-noted type incorporating manually shiftable features, such features can cause a jumping shift, for instance, a shift from first to third or first to fourth gears or vice versa, when the shift lever is operated once. In more recent years, some automotive manufacturers have incorporated automatic continuous variable transmissions wherein the gears are manually shiftable from one or two or more gears thus resulting in a jumping of the gears.